System and method for application of doppler corrections for time synchronized transmitter and receiver in motion

ABSTRACT

A system may include a transmitter node and a receiver node. Each node may include a communications interface including at least one antenna element and a controller operatively coupled to the communications interface, the controller including one or more processors, wherein the controller has information of own node velocity and own node orientation. Each node of the transmitter node and the receiver node may be in motion. Each node may be time synchronized to apply Doppler corrections associated with said node&#39;s own motions relative to a common reference frame. The common reference frame may be known to the transmitter node and the receiver node prior to the transmitter node transmitting signals to the receiver node and prior to the receiver node receiving the signals from the transmitter node.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims priority from thefollowing U.S. Patent Applications:

(a) U.S. patent application Ser. No. 17/233,107, filed Apr. 16, 2021,which is incorporated by reference in its entirety;

(b) P.C.T. Patent Application No. PCT/US22/24653, filed Apr. 13, 2022,which claims priority to U.S. patent application Ser. No. 17/233,107,filed Apr. 16, 2021, all of which are incorporated by reference in itsentirety;

(c) U.S. patent application Ser. No. 17/408,156, filed Aug. 20, 2021,which claims priority to U.S. patent application Ser. No. 17/233,107,filed Apr. 16, 2021, all of which are incorporated by reference in itsentirety;

(d) U.S. patent application Ser. No. 17/541,703, filed Dec. 3, 2021,which is incorporated by reference in its entirety, which claimspriority to:

-   -   1. U.S. patent application Ser. No. 17/408,156, filed Aug. 20,        2021, which is incorporated by reference in its entirety; and    -   2. U.S. patent application Ser. No. 17/233,107, filed Apr. 16,        2021, all of which is incorporated by reference in its entirety;

(e) U.S. patent application Ser. No. 17/534,061, filed Nov. 28, 2021,which is incorporated by reference in its entirety; and

(f) U.S. Patent Application No. 63/344,445, filed May 20, 2022, which isincorporated by reference in its entirety.

BACKGROUND

Mobile Ad-hoc NETworks (MANET; e.g., “mesh networks”) are known in theart as quickly deployable, self-configuring wireless networks with nopre-defined network topology. Each communications node within a MANET ispresumed to be able to move freely. Additionally, each communicationsnode within a MANET may be required to forward (relay) data packettraffic. Data packet routing and delivery within a MANET may depend on anumber of factors including, but not limited to, the number ofcommunications nodes within the network, communications node proximityand mobility, power requirements, network bandwidth, user trafficrequirements, timing requirements, and the like.

MANETs face many challenges due to the limited network awarenessinherent in such highly dynamic, low-infrastructure communicationsystems. Given the broad ranges in variable spaces, the challenges liein making good decisions based on such limited information. For example,in static networks with fixed topologies, protocols can propagateinformation throughout the network to determine the network structure,but in dynamic topologies this information quickly becomes stale andmust be periodically refreshed. It has been suggested that directionalsystems are the future of MANETs, but this future has not as yet beenrealized. In addition to topology factors, fast-moving platforms (e.g.,communications nodes moving relative to each other) experience afrequency Doppler shift (e.g., offset) due to the relative radialvelocity between each set of nodes. This Doppler frequency shift oftenlimits receive sensitivity levels which can be achieved by a node withina mobile network.

SUMMARY

A system may include a transmitter node and a receiver node. Each nodemay include a communications interface including at least one antennaelement and a controller operatively coupled to the communicationsinterface, the controller including one or more processors, wherein thecontroller has information of own node velocity and own nodeorientation. Each node of the transmitter node and the receiver node maybe in motion. Each node may be time synchronized to apply Dopplercorrections associated with said node's own motions relative to a commonreference frame. The common reference frame may be known to thetransmitter node and the receiver node prior to the transmitter nodetransmitting signals to the receiver node and prior to the receiver nodereceiving the signals from the transmitter node.

In a further aspect, a method may include: providing a transmitter nodeand a receiver node, wherein each node of the transmitter node and thereceiver node are time synchronized, wherein each node of thetransmitter node and the receiver node are in motion, wherein each nodeof the transmitter node and the receiver node comprises a communicationsinterface including at least one antenna element, wherein each node ofthe transmitter node and the receiver node further comprises acontroller operatively coupled to the communications interface, thecontroller including one or more processors, wherein the controller hasinformation of own node velocity and own node orientation; based atleast on the time synchronization, applying, by the transmitter node,Doppler corrections to the transmitter node's own motions relative to acommon reference frame; and based at least on the time synchronization,applying, by the receiver node, Doppler corrections to the receivernode's own motions relative to the common reference frame, wherein thecommon reference frame is known to the transmitter node and the receivernode prior to the transmitter node transmitting signals to the receivernode and prior to the receiver node receiving the signals from thetransmitter node.

This Summary is provided solely as an introduction to subject matterthat is fully described in the Detailed Description and Drawings. TheSummary should not be considered to describe essential features nor beused to determine the scope of the Claims. Moreover, it is to beunderstood that both the foregoing Summary and the following DetailedDescription are example and explanatory only and are not necessarilyrestrictive of the subject matter claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. The use of the same reference numbers in different instances inthe description and the figures may indicate similar or identical items.Various embodiments or examples (“examples”) of the present disclosureare disclosed in the following detailed description and the accompanyingdrawings. The drawings are not necessarily to scale. In general,operations of disclosed processes may be performed in an arbitraryorder, unless otherwise provided in the claims. In the drawings:

FIG. 1 is a diagrammatic illustration of a mobile ad hoc network (MANET)and individual nodes thereof according to example embodiments of thisdisclosure;

FIG. 2A is a graphical representation of frequency shift profiles withinthe MANET of FIG. 1,

FIG. 2B is a graphical representation of frequency shift profiles withinthe MANET of FIG. 1,

FIG. 3 is a diagrammatic illustration of a transmitter node and areceiver node according to example embodiments of this disclosure;

FIG. 4A is a graphical representation of frequency shift profiles withinthe MANET of FIG. 3;

FIG. 4B is a graphical representation of frequency shift profiles withinthe MANET of FIG. 3;

FIG. 5 is an exemplary graph of sets for covering space;

FIG. 6 is a diagrammatic illustration of a transmitter node and areceiver node according to example embodiments of this disclosure;

and FIG. 7 is a flow diagram illustrating a method according to exampleembodiments of this disclosure.

DETAILED DESCRIPTION

Before explaining one or more embodiments of the disclosure in detail,it is to be understood that the embodiments are not limited in theirapplication to the details of construction and the arrangement of thecomponents or steps or methodologies set forth in the followingdescription or illustrated in the drawings. In the following detaileddescription of embodiments, numerous specific details may be set forthin order to provide a more thorough understanding of the disclosure.However, it will be apparent to one of ordinary skill in the art havingthe benefit of the instant disclosure that the embodiments disclosedherein may be practiced without some of these specific details. In otherinstances, well-known features may not be described in detail to avoidunnecessarily complicating the instant disclosure.

As used herein a letter following a reference numeral is intended toreference an embodiment of the feature or element that may be similar,but not necessarily identical, to a previously described element orfeature bearing the same reference numeral (e.g., 1, 1 a, 1 b). Suchshorthand notations are used for purposes of convenience only and shouldnot be construed to limit the disclosure in any way unless expresslystated to the contrary.

Further, unless expressly stated to the contrary, “or” refers to aninclusive or and not to an exclusive or. For example, a condition A or Bis satisfied by any one of the following: A is true (or present) and Bis false (or not present), A is false (or not present) and B is true (orpresent), and both A and B are true (or present).

In addition, use of “a” or “an” may be employed to describe elements andcomponents of embodiments disclosed herein. This is done merely forconvenience and “a” and “an” are intended to include “one” or “at leastone,” and the singular also includes the plural unless it is obviousthat it is meant otherwise.

Finally, as used herein any reference to “one embodiment” or “someembodiments” means that a particular element, feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment disclosed herein. The appearances of thephrase “in some embodiments” in various places in the specification arenot necessarily all referring to the same embodiment, and embodimentsmay include one or more of the features expressly described orinherently present herein, or any combination or sub-combination of twoor more such features, along with any other features which may notnecessarily be expressly described or inherently present in the instantdisclosure.

Broadly speaking, embodiments of the inventive concepts disclosed hereinare directed to a method and a system including a transmitter node and areceiver node, which may be time synchronized to apply Dopplercorrections associated with said node's own motions relative to a commonreference frame.

In some embodiments, a stationary receiver may determine a cooperativetransmitter's direction and velocity vector by using a Doppler nullscanning approach in two dimensions. A benefit of the approach is thespatial awareness without exchanging explicit positional information.Other benefits include discovery, synchronization, and Dopplercorrections which are important for communications. Some embodiment maycombine coordinated transmitter frequency shifts along with thetransmitter's motion induced Doppler frequency shift to produce uniquenet frequency shift signal characteristics resolvable using a stationaryreceiver to achieve spatial awareness. Further, some embodiment mayinclude a three-dimensional (3D) approach with the receiver and thetransmitter in motion.

Some embodiments may use analysis performed in a common reference frame(e.g., a common inertial reference frame, such as the Earth, which mayignore the curvature of Earth), and it is assumed that thecommunications system for each of the transmitter and receiver isinformed by the platform of its own velocity and orientation. Theapproach described herein can be used for discovery and tracking, butthe discussion here focuses on discovery which is often the mostchallenging aspect.

The meaning of the Doppler Null′ can be explained in part through areview of the two-dimensional (2D) case without the receiver motion, andthen may be expounded on by a review of adding the receiver motion tothe 2D case, and then including receiver motion in the 3D case.

The Doppler frequency shift of a communications signal is proportionalto the radial velocity between transmitter and receiver, and anysignificant Doppler shift is typically a hindrance that should beconsidered by system designers. In contrast, some embodiments utilizethe Doppler effect to discriminate between directions with theresolution dictated by selected design parameters. Furthermore, suchembodiments use the profile of the net frequency shift as thepredetermined ‘Null’ direction scans through the angle space. Theresultant profile is sinusoidal with an amplitude that provides thetransmitter's speed, a zero net frequency shift when the ‘Null’direction aligns with the receiver, and a minimum indicating thedirection of the transmitter's velocity. It should be noted that thatthe transmitter cannot correct for Doppler in all directions at one timeso signal characteristics are different in each direction and aredifferent for different transmitter velocities as well. It is exactlythese characteristics that the receiver uses to determine spatialawareness. The received signal has temporal spatial characteristics thatcan be mapped to the transmitter's direction and velocity. This approachutilizes the concept of a ‘Null’ which is simply the direction where thetransmitter perfectly corrects for its own Doppler shift. The same‘Nulling’ protocol runs on each node and scans through all directions.Here we arbitrarily illustrate the scanning with discrete successivesteps of 10 degrees but in a real system; however, it should beunderstood that any suitable step size of degrees may be used forDoppler null scanning.

As already mentioned, one of the contributions of some embodiments ispassive spatial awareness. Traditionally, spatial information forneighbor nodes (based on a global positioning system (GPS) and/or gyrosand accelerometers) can be learned via data communication.Unfortunately, spatial awareness via data communication, referred to asactive spatial awareness is possible only after communication hasalready been established, not while discovering those neighbor nodes.Data communication is only possible after the signals for neighbor nodeshave been discovered, synchronized and Doppler corrected. In contrast,in some embodiments, the passive spatial awareness described herein maybe performed using only synchronization bits associated withacquisition. This process can be viewed as physical layer overhead andtypically requires much lower bandwidth compared to explicit datatransfers. The physical layer overheads for discovery, synchronizationand Doppler correction have never been utilized for topology learningfor upper layers previously.

Traditionally, network topology is harvested via a series of data packetexchanges (e.g., hello messaging and link status advertisements). Thepassive spatial awareness may eliminate hello messaging completely andprovide a wider local topology which is beyond the coverage of hellomessaging. By utilizing passive spatial awareness, highly efficientmobile ad hoc networking (MANET) is possible. Embodiments may improvethe functioning of a network, itself.

Referring to FIG. 1, a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104.

In embodiments, the multi-node communications network 100 may includeany multi-node communications network known in the art. For example, themulti-node communications network 100 may include a mobile ad-hocnetwork (MANET) in which the Tx and Rx nodes 102, 104 (as well as everyother communications node within the multi-node communications network)is able to move freely and independently. Similarly, the Tx and Rx nodes102, 104 may include any communications node known in the art which maybe communicatively coupled. In this regard, the Tx and Rx nodes 102, 104may include any communications node known in the art fortransmitting/transceiving data packets. For example, the Tx and Rx nodes102, 104 may include, but are not limited to, radios (such as on avehicle or on a person), mobile phones, smart phones, tablets, smartwatches, laptops, and the like. In embodiments, the Rx node 104 of themulti-node communications network 100 may each include, but are notlimited to, a respective controller 106 (e.g., control processor),memory 108, communication interface 110, and antenna elements 112. (Inembodiments, all attributes, capabilities, etc. of the Rx node 104described below may similarly apply to the Tx node 102, and to any othercommunication node of the multi-node communication network 100.)

In embodiments, the controller 106 provides processing functionality forat least the Rx node 104 and can include any number of processors,micro-controllers, circuitry, field programmable gate array (FPGA) orother processing systems, and resident or external memory for storingdata, executable code, and other information accessed or generated bythe Rx node 104. The controller 106 can execute one or more softwareprograms embodied in a non-transitory computer readable medium (e.g.,memory 108) that implement techniques described herein. The controller106 is not limited by the materials from which it is formed or theprocessing mechanisms employed therein and, as such, can be implementedvia semiconductor(s) and/or transistors (e.g., using electronicintegrated circuit (IC) components), and so forth.

In embodiments, the memory 108 can be an example of tangible,computer-readable storage medium that provides storage functionality tostore various data and/or program code associated with operation of theRx node 104 and/or controller 106, such as software programs and/or codesegments, or other data to instruct the controller 106, and possiblyother components of the Rx node 104, to perform the functionalitydescribed herein. Thus, the memory 108 can store data, such as a programof instructions for operating the Rx node 104, including its components(e.g., controller 106, communication interface 110, antenna elements112, etc.), and so forth. It should be noted that while a single memory108 is described, a wide variety of types and combinations of memory(e.g., tangible, non-transitory memory) can be employed. The memory 108can be integral with the controller 106, can comprise stand-alonememory, or can be a combination of both. Some examples of the memory 108can include removable and non-removable memory components, such asrandom-access memory (RAM), read-only memory (ROM), flash memory (e.g.,a secure digital (SD) memory card, a mini-SD memory card, and/or amicro-SD memory card), solid-state drive (SSD) memory, magnetic memory,optical memory, universal serial bus (USB) memory devices, hard diskmemory, external memory, and so forth.

In embodiments, the communication interface 110 can be operativelyconfigured to communicate with components of the Rx node 104. Forexample, the communication interface 110 can be configured to retrievedata from the controller 106 or other devices (e.g., the Tx node 102and/or other nodes), transmit data for storage in the memory 108,retrieve data from storage in the memory, and so forth. Thecommunication interface 110 can also be communicatively coupled with thecontroller 106 to facilitate data transfer between components of the Rxnode 104 and the controller 106. It should be noted that while thecommunication interface 110 is described as a component of the Rx node104, one or more components of the communication interface 110 can beimplemented as external components communicatively coupled to the Rxnode 104 via a wired and/or wireless connection. The Rx node 104 canalso include and/or connect to one or more input/output (I/O) devices.In embodiments, the communication interface 110 includes or is coupledto a transmitter, receiver, transceiver, physical connection interface,or any combination thereof.

It is contemplated herein that the communication interface 110 of the Rxnode 104 may be configured to communicatively couple to additionalcommunication interfaces 110 of additional communications nodes (e.g.,the Tx node 102) of the multi-node communications network 100 using anywireless communication techniques known in the art including, but notlimited to, GSM, GPRS, CDMA, EV-DO, EDGE, WiMAX, 3G, 4G, 4G LTE, 5G,WiFi protocols, RF, LoRa, and the like.

In embodiments, the antenna elements 112 may include directional oromnidirectional antenna elements capable of being steered or otherwisedirected (e.g., via the communications interface 110) for spatialscanning in a full 360-degree arc (114) relative to the Rx node 104.

In embodiments, the Tx node 102 and Rx node 104 may both be moving in anarbitrary direction at an arbitrary speed, and may similarly be movingrelative to each other. For example, the Tx node 102 may be movingrelative to the Rx node 104 according to a velocity vector 116, at arelative velocity VTX and a relative angular direction (an angle αrelative to an arbitrary direction 118 (e.g., due east); 8 may be theangular direction of the Rx node relative to due east.

In embodiments, the Tx node 102 may implement a Doppler nullingprotocol. For example, the Tx node 102 may adjust its transmit frequencyto counter the Doppler frequency offset such that there is no netfrequency offset (e.g., “Doppler null”) in a Doppler nulling direction120 (e.g., at an angle ϕ relative to the arbitrary direction 118). Thetransmitting waveform (e.g., the communications interface 110 of the Txnode 102) may be informed by the platform (e.g., the controller 106) ofits velocity vector and orientation (e.g., a, V_(T)) and may adjust itstransmitting frequency to remove the Doppler frequency shift at eachDoppler nulling direction 120 and angle φ.

To illustrate aspects of some embodiments, we show the 2D dependence ofthe net frequency shift for a stationary receiver as a function of Nulldirection across the horizon, as shown in a top-down view of FIG. 1,where the receiver node 104 is stationary and positioned 8 from eastrelative to the transmitter, the transmitter node 102 is moving with aspeed |{right arrow over (V_(T))}| and direction a from east and asnapshot of the scanning ϕ which is the ‘Null’ direction, exemplarilyshown as 100 degrees in this picture.

The Doppler shift is a physical phenomenon due to motion and can beconsidered as a channel effect. In this example the transmitter node 102is the only moving object, so it is the only source of Doppler shift.The Doppler frequency shift as seen by the receiver node 104 due to thetransmitter node 102 motion is:

${\frac{\Delta f_{DOPPLER}}{f} = {\frac{❘\overset{\longrightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}}},$

where c is the speed of light

The other factor is the transmitter frequency adjustment term thatshould exactly compensate the Doppler shift when the ‘Null’ directionaligns with the receiver direction. It is the job of the transmitternode 102 to adjust its transmit frequency according to its own speed(|{right arrow over (V_(T))}|), and velocity direction (α). Thattransmitter frequency adjustment (Δf_(T)) is proportional to thevelocity projection onto the ‘Null’ direction (ϕ) and is:

$\frac{\Delta f_{T}}{f} = {- \frac{❘\overset{\longrightarrow}{V_{T}}❘}{c}{\cos\left( {\varphi - \alpha} \right)}}$

The net frequency shift seen by the receiver is the sum of the twoterms:

$\frac{\Delta f_{net}}{f} = {\frac{❘\overset{\longrightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack}$

It is assumed that the velocity vector and the direction changes slowlycompared to the periodic measurement of Δf_(net). Under thoseconditions, the unknown parameters (from the perspective of the receivernode 104) of α, |{right arrow over (V_(T))}|, and θ are constants.

Furthermore, it is assumed that the receiver node 104 has animplementation that resolves the frequency of the incoming signal, aswould be understood to one of ordinary skill in the art.

FIG. 2A shows the resulting net frequency shift as a function of the‘Null’ direction for scenarios where a stationary receiver is East ofthe transmitter (theta=0), and with a transmitter speed of 1500 metersper second (m/s). FIG. 2B shows the results for a stationary receiverand for several directions with an Eastern transmitter node velocitydirection (alpha=0). The frequency shifts are in units of parts permillion (ppm). As shown in FIGS. 2A and 2B, the amplitude is consistentwith the transmitter node's 102 speed of 5 ppm [|{right arrow over(V_(T))}|/c*(1×10⁶)] regardless of the velocity direction or position,the net frequency shift is zero when the ‘Null’ angle is in the receiverdirection (when ϕ=θ), and the minimum occurs when the ‘Null’ is alignedwith the transmitter node's 102 velocity direction (when ϕ=α).

From the profile, the receiver node 104 can therefore determine thetransmitter node's 102 speed, the transmitter node's 102 heading, andthe direction of the transmitter node 102 is known to at most, one oftwo locations (since some profiles have two zero crossings). It shouldbe noted that the two curves cross the y axis twice (0 & 180 degrees inFIG. 2A, and ±90 degrees in FIG. 2B) so there is initially an instanceof ambiguity in position direction. In this case the receiver node 104knows the transmitter node 102 is either East or West of the receivernode 104.

Referring to FIG. 3, a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104. As shown in FIG. 3 both of the transmitter node102 and the receiver node 104 are in motion in two dimensions.

The simultaneous movement scenario is depicted in FIG. 3 where thereceiver node 104 is also moving in a generic velocity characterized bya speed |{right arrow over (V_(R))}| and the direction, θ. The protocolfor the moving receiver node 104 incorporates a frequency adjustment onthe receiver node's 104 side to compensate for the receiver node's 104motion as well. The equations have two additional terms. One is aDoppler term for the motion of the receiver and the second is frequencycompensation by the receiver.

Again, the Doppler shift is a physical phenomenon due to motion and canbe considered as a channel effect, but in this case both the transmitternode 102 and the receiver node 104 are moving so there are two Dopplershift terms. The true Doppler shift as seen by the receiver due to therelative radial velocity is:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{❘\overset{\longrightarrow}{V_{T}}❘}{c}{\cos\left( {\theta - \alpha} \right)}} - {\frac{❘\overset{\longrightarrow}{V_{R}}❘}{c}{\cos\left( {\theta - \beta} \right)}}}$

The other factors are the transmitter node 102 and receiver node 104frequency adjustment terms that exactly compensates the Doppler shiftwhen the ‘Null’ direction aligns with the receiver direction. It is thejob of the transmitter node 102 to adjust the transmitter node's 102transmit frequency according to its own speed (|{right arrow over(V_(T))}|), and velocity direction (α). That transmitter node frequencyadjustment is proportional to the velocity projection onto the ‘Null’direction (ϕ) and is the first term in the equation below.

It is the job of the receiver node 104 to adjust the receiver nodefrequency according to the receiver node's 104 own speed (|{right arrowover (V_(R))}|I), and velocity direction (β). That receiver nodefrequency adjustment is proportional to the velocity projection onto the‘Null’ direction (ϕ) and is the second term in the equation below. Thereceiver node frequency adjustment can be done to the receive signalprior to the frequency resolving algorithm or could be done within thealgorithm.

$\frac{\Delta f_{{T\&}R}}{f} = {{- \frac{❘\overset{\longrightarrow}{V_{T}}❘}{c}{\cos\left( {\varphi - \alpha} \right)}} + {\frac{❘\overset{\longrightarrow}{V_{R}}❘}{c}{\cos\left( {\varphi - \beta} \right)}}}$

The net frequency shift seen by the receiver is the sum of all terms:

$\frac{\Delta f_{net}}{f} = {{\frac{❘\overset{\longrightarrow}{V_{T}}❘}{c}\left\lbrack {{\cos\left( {\theta - \alpha} \right)} - {\cos\left( {\varphi - \alpha} \right)}} \right\rbrack} - {\frac{❘\overset{\longrightarrow}{V_{R}}❘}{c}\left\lbrack {{\cos\left( {\theta - \beta} \right)} - {\cos\left( {\varphi - \beta} \right)}} \right\rbrack}}$

Again, it is assumed that the receiver node 104 has an implementationthat resolves the frequency of the incoming signal, as would beunderstood in the art.

Also, it is assumed that the velocity vector and direction changesslowly compared to the periodic measurement of Δf_(net). Again, undersuch conditions, the unknown parameters (from the perspective of thereceiver node 104) α, |{right arrow over (V_(T))}|, and θ are constants.

The net frequency shift for the two-dimensional (2D) moving receivernode 104 approach is shown in FIGS. 4A and 4B for several scenario casesof receiver node location, θ, and transmitter node and receiver nodespeeds (|{right arrow over (V_(T))}| & |{right arrow over (V_(R))}|), aswell as transmitter node and receiver node velocity direction (α and β).FIG. 4A has different speeds for the transmitter node 102 and receivernode 104 as well as the receiver node location of θ=0. FIG. 4B has thesame speed for the transmitter node and receiver node. Similarly, thereare three concepts to notice here:

-   -   The amplitude is consistent with the relative velocity between        transmitter node 102 and receiver node 104 [|(|{right arrow over        (V_(T))}| cos (α)−|{right arrow over (V_(R))}| cos        (β))|/c*(1e6)].    -   The net frequency shift is zero when the ‘Null’ angle is in the        receiver direction (when ϕ=θ).    -   The minimum occurs when the ‘Null’ is aligned with the relative        velocity direction (when ϕ=angle (|{right arrow over (V_(T))}|        cos (α)−|{right arrow over (V_(R))}| cos (β))).

Again, there is an initial dual point ambiguity with the position, θ,but the transmitter node's 102 speed and velocity vector is known.

Referring now to FIG. 5, while the 2D picture is easier to visualize,the same principles apply to the 3D case. FIG. 5 shows a number ofdirection sets needed to span 3D and 2D space with different cone sizes(cone sizes are full width). Before diving into the equations, it'sworth commenting on the size of the space when including anotherdimension. For example, when a ‘Null’ step size of 10 degrees was usedin the previous examples, it took 36 sets to span the 360 degrees in 2D.Thus, if an exemplary detection angle of 10 degrees is used (e.g., adirectional antenna with 10-degree cone) it would take 36 sets to coverthe 2D space. The 3D fractional coverage can be computed by calculatingthe coverage of a cone compared to the full 4 pi steradians. Thefraction is equal to the integral

${FractionCoverage3D} = {\frac{\int_{0}^{{ConeSize}/2}{r^{2}{\sin({\theta\prime})}d{\theta\prime}d\varphi}}{4\pi r^{2}} = \frac{1 - {\cos\left( {{ConeSize}/2} \right)}}{2}}$FractionCoverage2D = 2π/ConeSize

The number of sets to span the space is shown in FIG. 5 for both the 2Dand 3D cases which correlates with discovery time. Except for narrowcone sizes, the number of sets is not drastically greater for the 3Dcase (e.g., approximately 15 times at 10 degrees, 7.3 time at 20degrees, and around 4.9 times at 30 degrees). Unless systems are limitedto very narrow cone sizes, the discovery time for 3D searches is notoverwhelming compared to a 2D search.

Referring now to FIG. 6, a multi-node communications network 100 isdisclosed. The multi-node communications network 100 may includemultiple communications nodes, e.g., a transmitter (Tx) node 102 and areceiver (Rx) node 104. As shown in FIG. 6 both of the transmitter node102 and the receiver node 104 are in motion in three dimensions.

The 3D approach to Doppler nulling follows the 2D approach but it isillustrated here with angles and computed vectorially for simplicity.

In three dimensions, it is convenient to express the equations in vectorform which is valid for 2 or 3 dimensions. FIG. 6 shows the geometry in3 dimensions where

is the unit vector pointing to the receiver from the transmitter, and

is the unit vector pointing in the ‘Null’ direction defined by theprotocol.

The true Doppler shift as seen by the receiver node 104 due to therelative radial velocity which is the projection onto the

vector:

$\frac{\Delta f_{DOPPLER}}{f} = {{\frac{1}{c}{\overset{\longrightarrow}{V_{T}} \cdot \overset{︷}{Direction}}} - {\frac{1}{c}{\overset{\longrightarrow}{V_{R}} \cdot \overset{︷}{Direction}}}}$

The nulling protocol adjusts the transmit node frequency and receivernode frequency due to their velocity projections onto the

direction

$\frac{\Delta f_{T}}{f} = {{- \frac{1}{c}{\overset{\longrightarrow}{V_{T}} \cdot \overset{︷}{Null}}} + {\frac{1}{c}{\overset{\longrightarrow}{V_{R}} \cdot \overset{︷}{Null}}}}$

The net frequency shift seen by the receiver node 104 is the sum of allterms:

$\frac{\Delta f_{net}}{f} = {{\frac{1}{c}{\overset{\longrightarrow}{V_{T}} \cdot \overset{︷}{Direction}}} - {\frac{1}{c}{\overset{\longrightarrow}{V_{R}} \cdot \overset{︷}{Direction}}} - {\frac{1}{c}{\overset{\longrightarrow}{V_{T}} \cdot \overset{︷}{Null}}} + {\frac{1}{c}{\overset{\longrightarrow}{V_{R}} \cdot \overset{︷}{Null}}}}$

The net frequency shift for the 3D moving receiver node 104 approach isnot easy to show pictorially but can be inspected with mathematicalequations to arrive at useful conclusions. The first two terms are theDoppler correction (DC) offset and the last two terms are the nulldependent terms. Since the

is the independent variable, the maximum occurs when ({right arrow over(V_(R))}−{right arrow over (V_(T))}) and

are parallel and is a minimum when they are antiparallel. Furthermore,the relative speed is determined by the amplitude,

${Amplitude} = {\frac{1}{c}{❘{\overset{\longrightarrow}{V_{R}} - \overset{\longrightarrow}{V_{T}}}❘}}$

Lastly, the net frequency is zero when the

is parallel (i.e., parallel in same direction, as opposed toanti-parallel) to

.

${\frac{\Delta f_{net}}{f} = {0{when}}},{{{\frac{1}{c}{\overset{\longrightarrow}{V_{T}} \cdot \overset{︷}{Direction}}} - {\frac{1}{c}{\overset{\longrightarrow}{V_{R}} \cdot \overset{︷}{Direction}}}} = {{\frac{1}{c}{\overset{\longrightarrow}{V_{T}} \cdot \overset{︷}{Null}}} - {\frac{1}{c}{\overset{\longrightarrow}{V_{R}} \cdot \overset{︷}{Null}}}}}$${or},{{\left( {\overset{\longrightarrow}{V_{T}} - \overset{\longrightarrow}{V_{R}}} \right) \cdot \overset{︷}{Direction}} = {\left( {\overset{\longrightarrow}{V_{T}} - \overset{\longrightarrow}{V_{R}}} \right) \cdot \overset{︷}{Null}}}$

For the 3D case:

-   -   The amplitude is consistent with the relative velocity between        transmitter node 102 and receiver node 104 [|{right arrow over        (V_(R))}|−|{right arrow over (V_(T))}|/c].    -   The net frequency shift is zero when the ‘Null’ angle is in the        receiver node direction, ({right arrow over (V_(T))}−{right        arrow over (V_(R))})·        =({right arrow over (V_(T))}−{right arrow over (V_(R))})·        ).    -   The minimum occurs when the ‘Null’ is aligned with the relative        velocity direction.

Referring still to FIG. 6, in some embodiments, the system (e.g., themulti-node communications network 100) may include a transmitter node102 and a receiver node 104. Each node of the transmitter node 102 andthe receiver node 104 may include a communications interface 110including at least one antenna element 112 and a controller operativelycoupled to the communications interface, the controller 106 includingone or more processors, wherein the controller 106 has information ofown node velocity and own node orientation. The transmitter node 102 andthe receiver node 104 may be in motion (e.g., in two dimensions or inthree dimensions). The transmitter node 102 and the receiver node 104may be time synchronized to apply Doppler corrections associated withsaid node's own motions relative to a common reference frame (e.g., acommon inertial reference frame (e.g., a common inertial reference framein motion or a stationary common inertial reference frame)). The commonreference frame may be known to the transmitter node 102 and thereceiver node 104 prior to the transmitter node 102 transmitting signalsto the receiver node 104 and prior to the receiver node 104 receivingthe signals from the transmitter node 102. In some embodiments, thesystem is a mobile ad-hoc network (MANET) comprising the transmitternode 102 and the receiver node 104.

In some embodiments, the transmitter node 102 and the receiver node 104are time synchronized via synchronization bits associated withacquisition. For example, the synchronization bits may operate asphysical layer overhead.

In some embodiments, the transmitter node 102 is configured to adjust atransmit frequency according to an own speed and an own velocitydirection of the transmitter node 102 so as to perform atransmitter-side Doppler correction. In some embodiments, the receivernode 104 is configured to adjust a receiver frequency of the receivernode 104 according to an own speed and an own velocity direction of thereceiver node 104 so as to perform a receiver-side Doppler correction.In some embodiments, an amount of adjustment of the adjusted transmitfrequency is proportional to a transmitter node 102 velocity projectiononto a Doppler null direction, wherein an amount of adjustment of theadjusted receiver frequency is proportional to a receiver node 104velocity projection onto the Doppler null direction. In someembodiments, the receiver node 102 is configured to determine a relativespeed between the transmitter node 102 and the receiver node 104. Insome embodiments, the receiver node 104 is configured to determine adirection that the transmitter node 102 is in motion and a velocityvector of the transmitter node 102. In some embodiments, a maximum netfrequency shift for a Doppler correction by the receiver node 104 occurswhen a resultant vector is parallel to the Doppler null direction,wherein the resultant vector is equal to a velocity vector of thereceiver node 104 minus the velocity vector of the transmitter node 102.In some embodiments, a minimum net frequency shift for a Dopplercorrection by the receiver node 104 occurs when a resultant vector isantiparallel to the Doppler null direction, wherein the resultant vectoris equal to a velocity vector of the receiver node 104 minus thevelocity vector of the transmitter node 102. In some embodiments, a netfrequency shift for a Doppler correction by the receiver node 104 iszero when a vector pointing to the receiver node from the transmitternode 102 is parallel to the Doppler null direction.

Referring now to FIG. 7, an exemplary embodiment of a method 700according to the inventive concepts disclosed herein may include one ormore of the following steps. Additionally, for example, some embodimentsmay include performing one or more instances of the method 700iteratively, concurrently, and/or sequentially. Additionally, forexample, at least some of the steps of the method 700 may be performedin parallel and/or concurrently. Additionally, in some embodiments, atleast some of the steps of the method 700 may be performednon-sequentially.

A step 702 may include providing a transmitter node and a receiver node,wherein each node of the transmitter node and the receiver node are timesynchronized, wherein each node of the transmitter node and the receivernode are in motion, wherein each node of the transmitter node and thereceiver node comprises a communications interface including at leastone antenna element, wherein each node of the transmitter node and thereceiver node further comprises a controller operatively coupled to thecommunications interface, the controller including one or moreprocessors, wherein the controller has information of own node velocityand own node orientation.

A step 704 may include based at least on the time synchronization,applying, by the transmitter node, Doppler corrections to thetransmitter node's own motions relative to a common reference frame.

A step 706 may include based at least on the time synchronization,applying, by the receiver node, Doppler corrections to the receivernode's own motions relative to the common reference frame, wherein thecommon reference frame is known to the transmitter node and the receivernode prior to the transmitter node transmitting signals to the receivernode and prior to the receiver node receiving the signals from thetransmitter node.

Further, the method 700 may include any of the operations disclosedthroughout.

The null scanning technique discussed herein illustrates a system and amethod for spatial awareness from resolving the temporal spatialcharacteristics of the transmitter node's 102 radiation. This approachinforms the receiver node 104 of the relative speed between thetransmitter node 102 and receiver node 104 as well as the transmitternode direction and transmitter node velocity vector. This approachincludes scanning through all directions and has a high sensitivity(e.g., low net frequency shift) when the null direction is aligned withthe transmitter node direction. This approach can be implemented on ahighly sensitive acquisition frame which is typically much moresensitive than explicit data transfers which allow for theultra-sensitive spatial awareness with relatively low power.

CONCLUSION

It is to be understood that embodiments of the methods disclosed hereinmay include one or more of the steps described herein. Further, suchsteps may be carried out in any desired order and two or more of thesteps may be carried out simultaneously with one another. Two or more ofthe steps disclosed herein may be combined in a single step, and in someembodiments, one or more of the steps may be carried out as two or moresub-steps. Further, other steps or sub-steps may be carried in additionto, or as substitutes to one or more of the steps disclosed herein.

Although inventive concepts have been described with reference to theembodiments illustrated in the attached drawing figures, equivalents maybe employed and substitutions made herein without departing from thescope of the claims. Components illustrated and described herein aremerely examples of a system/device and components that may be used toimplement embodiments of the inventive concepts and may be replaced withother devices and components without departing from the scope of theclaims. Furthermore, any dimensions, degrees, and/or numerical rangesprovided herein are to be understood as non-limiting examples unlessotherwise specified in the claims.

We claim:
 1. A system, comprising: a transmitter node and a receivernode, wherein each node of the transmitter node and the receiver nodecomprises: a communications interface including at least one antennaelement; and a controller operatively coupled to the communicationsinterface, the controller including one or more processors, wherein thecontroller has information of own node velocity and own nodeorientation; wherein each node of the transmitter node and the receivernode are in motion, wherein each node of the transmitter node and thereceiver node are time synchronized to apply Doppler correctionsassociated with said node's own motions relative to a common referenceframe, wherein the common reference frame is known to the transmitternode and the receiver node prior to the transmitter node transmittingsignals to the receiver node and prior to the receiver node receivingthe signals from the transmitter node.
 2. The system of claim 1, whereinthe common reference frame is a common inertial reference frame.
 3. Thesystem of claim 2, wherein the common inertial reference frame is inmotion.
 4. The system of claim 1, wherein the transmitter node isconfigured to adjust a transmit frequency according to an own speed andan own velocity direction of the transmitter node so as to perform atransmitter-side Doppler correction.
 5. The system of claim 4, whereinthe receiver node is configured to adjust a receiver frequency of thereceiver node according to an own speed and an own velocity direction ofthe receiver node so as to perform a receiver-side Doppler correction.6. The system of claim 5, wherein an amount of adjustment of theadjusted transmit frequency is proportional to a transmitter nodevelocity projection onto a Doppler null direction, wherein an amount ofadjustment of the adjusted receiver frequency is proportional to areceiver node velocity projection onto the Doppler null direction. 7.The system of claim 6, wherein the receiver node is configured todetermine a relative speed between the transmitter node and the receivernode.
 8. The system of claim 7, wherein the receiver node is configuredto determine a direction that the transmitter node is in motion and avelocity vector of the transmitter node.
 9. The system of claim 8,wherein a maximum net frequency shift for a Doppler correction by thereceiver node occurs when a resultant vector is parallel to the Dopplernull direction, wherein the resultant vector is equal to a velocityvector of the receiver node minus the velocity vector of the transmitternode.
 10. The system of claim 8, wherein a minimum net frequency shiftfor a Doppler correction by the receiver node occurs when a resultantvector is antiparallel to the Doppler null direction, wherein theresultant vector is equal to a velocity vector of the receiver nodeminus the velocity vector of the transmitter node.
 11. The system ofclaim 8, wherein a net frequency shift for a Doppler correction by thereceiver node is zero when a vector pointing to the receiver node fromthe transmitter node is parallel to the Doppler null direction.
 12. Thesystem of claim 1, wherein the transmitter node and the receiver nodeare time synchronized via synchronization bits associated withacquisition.
 13. The system of claim 12, wherein the synchronizationbits operate as physical layer overhead.
 14. The system of claim 1,wherein each node of the transmitter node and the receiver node are inmotion in three dimensions.
 15. The system of claim 1, wherein each nodeof the transmitter node and the receiver node are in motion in twodimensions.
 16. The system of claim 1, wherein the system is a mobilead-hoc network (MANET) comprising the transmitter node and the receivernode.
 17. A method, comprising: providing a transmitter node and areceiver node, wherein each node of the transmitter node and thereceiver node are time synchronized, wherein each node of thetransmitter node and the receiver node are in motion, wherein each nodeof the transmitter node and the receiver node comprises a communicationsinterface including at least one antenna element, wherein each node ofthe transmitter node and the receiver node further comprises acontroller operatively coupled to the communications interface, thecontroller including one or more processors, wherein the controller hasinformation of own node velocity and own node orientation; based atleast on the time synchronization, applying, by the transmitter node,Doppler corrections to the transmitter node's own motions relative to acommon reference frame; and based at least on the time synchronization,applying, by the receiver node, Doppler corrections to the receivernode's own motions relative to the common reference frame; wherein thecommon reference frame is known to the transmitter node and the receivernode prior to the transmitter node transmitting signals to the receivernode and prior to the receiver node receiving the signals from thetransmitter node.
 18. The method of claim 17, further comprising:adjusting, by the receiver node, a receiver frequency of the receivernode according to an own speed and an own velocity direction of thereceiver node so as to perform a receiver-side Doppler correction. 19.The method of claim 18, wherein an amount of adjustment of the adjustedtransmit frequency is proportional to a transmitter node velocityprojection onto a Doppler null direction, wherein an amount ofadjustment of the adjusted receiver frequency is proportional to areceiver node velocity projection onto the Doppler null direction. 20.The method of claim 19, further comprising: determining, by the receivernode, a relative speed between the transmitter node and the receivernode; and determining, by the receiver node, a direction that thetransmitter node is in motion and a velocity vector of the transmitternode.